1. Technical Field of the Invention
The present invention relates to grinding machines and to methods of machining workpieces having at least one eccentric diametral portion, such as crankshafts or the like. More particularly, the present invention relates to grinding machines and to methods of machining workpieces having at least one eccentric diametral portion wherein an apparatus is provided to position a device, such as a coolant nozzle, an in-process gauge, a workpiece support, or the like, near the workpiece during a machining operation.
2. Brief Description of the Related Art
With reference to FIG. 1, a conventional grinding machine 10 for machining generally cylindrical workpieces 20 includes a workpiece carrier 12 having aligned headstock 14 and footstock 16 positioned relative to one another along a carrier axis “C”. The headstock 14 and footstock 16 are configured to mount the workpiece 20 therebetween for powered rotation of the workpiece 20 about the carrier axis “C”. Workpiece 20 includes a workpiece axis “W” (FIG. 2) which typically is coincident with the carrier axis “C” when the workpiece 20 is mounted between the headstock 14 and the footstock 16.
A typical grinding machine 10 also includes a wheelhead 30 having a spindle 31 fixedly mounted thereto for driving the rotation of a grinding wheel 32 in a first direction ωG (FIG. 2) about a grinding wheel axis “G”. The wheel axis “G” typically is parallel to the carrier axis “C”, and thus, parallel to the workpiece axis “W”, although it may be oriented at some angle relative thereto. Workpiece 20 typically is rotated about its workpiece axis “W” in a second direction ωW (FIG. 2) opposite the first direction ωG at a rate less than the rate at which the grinding wheel 32 is rotated.
Typically, the wheelhead 30 is mounted on one or more slides 34 to permit reciprocating translation of the wheelhead 30 towards and away from the workpiece 20 along a slide direction “S”, which may be perpendicular to the carrier axis “C”, although it may alternatively be oriented at some angle relative thereto. The arrangement described above and shown in FIG. 1 is ideal for machining workpieces 20 having constant cross-section portions centered on-axis to the workpiece axis “W”, such as large shafts (which may include one or more stepped portions, as shown in FIG. 1) or such as the mainbearings 42 of a crankshaft 40 (which is shown in greater detail in FIG. 3). During a machining operation, the wheelhead 30 moves under programmed control along the slide direction “S” at some preselected rate chosen to provide a desired rate of material removal from the workpiece 20.
With additional reference now to FIG. 2, it oftentimes is desirable to position one or more devices near the workpiece 20 during some machining operations. For example, a coolant nozzle 50 (shown partially) may be mounted fixedly to the wheelhead 30 by conventional means (not shown) and positioned thereon to direct a flow of coolant generally in a path along a fluid direction “F”. Fluid path “F” directs coolant towards a portion of the workpiece 20 being machined for the purpose of dissipating heat generated during the machining operation and also for the purpose of flushing material removed from the workpiece 20 during machining. Similarly, an in-process gauge (not shown) may be mounted to the wheelhead 30 either alone or together with the coolant nozzle 50 and positioned thereon to engage the portion of the workpiece 20 being machined, for example, for the purpose of measuring the diameter of the workpiece 20 as it is being machined.
Regardless of the type of device mounted to the machine 10, in the case of a workpiece 20 having constant cross-section portions (or having cross-section portions with very little eccentricity), the grinding wheel-workpiece interface “P” (which is represented herein as a point located in two dimensional space) remains substantially unchanged during the entire machining operation. This is because the workpiece 20 (which rotates about its workpiece axis “W”) and the grinding wheel 32 (which rotates about its wheel axis “G”) do not move substantially relative to one another during a complete machining operation or cycle. Accordingly, the coolant nozzle 50, for example, may be mounted to the wheelhead 30 and positioned in a fixed orientation relative to the wheelhead 30 to direct coolant therefrom towards the contact point “P”. Because the location of the contact point “P” does not change substantially during such machining operations, the coolant nozzle 50 will continue to direct coolant along the generally-unchanging path “F” towards the contact point “P” substantially at all times during the machining operation without substantial variation.
However, in the case of a workpiece having cross-sectional portions with large degrees of eccentricity or in the case of a workpiece having portions thereof which orbit about the workpiece axis “W” along an outward path (such as in the case of crankshaft crankpins), the grinding wheel-workpiece contact point exhibits significant variation during an entire machining cycle.
For example, referring now to FIG. 3, a typical crankshaft 40 includes one or more generally cylindrical coaxial mainbearings 42 spaced along a mainbearing axis “MB” and one or more generally cylindrical crankpins 44 located between mainbearings 42 and rigidly connected thereto by one or more crankarms 46. Each crankpin 44 includes a crankpin axis “CP”, which is oriented parallel to the mainbearing axis “MB” and is spaced radially therefrom by some preselected distance. All crankpin axes “CP” may be aligned along a single axis, although it is typical for the crankpins 44 to be spaced at intervals equidistantly around the mainbearing axis “MB”. Crankarms 46 may include counterweights 48 located opposite crankpins 44 and positioned radially outwardly from the mainbearing axis “CB” so as to minimize the effects of rotational inertia due to motion of the crankpins 44 about the mainbearing axis “MB”.
With additional reference now to FIGS. 4 and 5, each crankpin 44 (and thus, each crankpin axis “CP”) will follow a circular path “R” about the mainbearing axis “MB” during each rotation of the crankshaft 40 (shown in phantom lines). During a complete machining operation, the crankshaft 42 is rotated one or more times about the mainbearing axis “MB”, and the grinding wheel 32 is moved controllably towards and away from the crankpin 44 along direction “S” during each rotation of the crankshaft 40 in unison therewith so as to maintain the point of contact “P” with the crankpin 44 as it orbits the mainbearing axis “MB”. The cooperating motion of translation of the grinding wheel 32 together with rotation of the crankshaft 40 results in the crankpin 44 moving relative to the grinding wheel 32 reciprocally along an arcuate path “T” having a radius “rT” centered on the wheel axis “G”. That is, the grinding wheel 32 (and the wheelhead 30 to which the grinding wheel 32 is mounted) “sees” the crankpin 44 moving reciprocally up and down along the arcuate path “T”. The grinding wheel-workpiece contact point “P”, then, travels along a similar reciprocating path (not shown) on the outer surface of the grinding wheel 32.
As mentioned above, during grinding operations where the grinding wheel-workpiece contact point does not change substantially (such as where constant cross-section workpieces are being machined), certain devices, such as coolant nozzles, may be mounted in fixed relation to the wheelhead and will operate at all times during the machining cycle for their intended purpose. However, it has been observed that during machining operations where the grinding wheel-workpiece contact point changes substantially (such as where eccentric or non-constant cross-section workpieces are being machined), those same devices may not operate for their intended purpose at all times during the machining cycle. Accordingly, it is desirable to provide an apparatus for mounting a device to a grinding machine such that the device operates for its intended purpose at substantially all times during the machining cycle.
It also has been observed that the operation and performance of some devices, such as in-process gauges and/or workpiece supports, which are intended to engage the workpiece directly during the machining operation are enhanced if the motion of the device resembles motion of the workpiece relative to the wheelhead. For example, U.S. Pat. No. 6,067,721 to Dall'Aglio, et al., teaches an in-process gauge mounted to a wheelhead of a grinding machine for positioning the gauge near an orbiting workpiece. The apparatus of Dall'Aglio '721, however, does not pivot directly about the center of the arcuate path along which the workpiece travels relative to the grinding wheel. As such, the apparatus consists of a complex linkage which is constrained in its motion and requires superfluous degrees of motion (relative to the workpiece) in which to operate. It is desirable therefore to provide an apparatus for mounting a device to a grinding machine such that the orientation and motion of the device mimics the orientation and motion of the workpiece during the machining cycle.
It is desirable furthermore to provide an apparatus for mounting a device to a grinding machine such that the orientation and motion of the device mimics the orientation and motion of the workpiece during the machining cycle, wherein the workpiece travels along an orbital or eccentric path during the machining cycle.
It is desirable furthermore to provide an apparatus for mounting a device to a grinding machine adapted to machine selected portions of crankshafts and of other orbiting and eccentric workpieces.
It is desirable furthermore to provide an apparatus for delivering coolant to a machining zone of a grinding machine.
It is desirable furthermore to provide an apparatus for positioning a workpiece support device near a workpiece being machined.
It is desirable furthermore to provide an apparatus for positioning an in-process gauge device near a workpiece being machined.
It is desirable furthermore to provide an apparatus for positioning various devices near a workpiece during machining operations such that the device maintains contact with the workpiece for substantially the entire machining operation.
It is desirable furthermore to provide an apparatus for positioning various devices near a workpiece during machining operations, wherein the apparatus is adapted to manually or automatedly disengaged the workpiece when commanded.
It is even further desirable to provide an apparatus for positioning various devices near a workpiece during machining operations, wherein motion of the apparatus has a minimum number of degrees of freedom with reference to motion of the workpiece, and preferably, has only a single degree of freedom with reference to motion of the grinding machine or a portion thereof, such as the wheelhead.